Public Lab Research note


Updated initial NDVI results from A1200 with internal Wratten 25

by patcoyle | February 22, 2014 05:24 | 3,176 views | 12 comments | #10055 | 3,176 views | 12 comments | #10055 22 Feb 05:24

Read more: publiclab.org/n/10055


What I want to do

Motivated by Chris Fastie and Ned Horning's work, change internal filter on A1200 from exposed color film (for NIR two-camera approach) to Wratten 25. I already tried the Wratten 25 as an external filter on an A490. However, I wanted to mount the gel film inside to protect it. Try it for NDVI.

(Updated: 1. Took 85 more test images, revealing internal blemish in some specific lighting conditions. Not sure if it is a fingerprint on filter or sensor, or something else. Most images appear ok 2. In response to comment tried processing without stretching vis or NIR using Ned Hornings Fiji tool)

My attempt and results

Updated as noted above: Composite showing example images with blemish:

image_issue_crpd.jpg

Contact sheet views of as shot images, mostly ok and portion of processed images:

input_images.jpg

output_images.jpg

Composite image showing result of processing without stretching vis or NIR using Ned Hornings Fiji tool

test_w__wo_stretching_all.jpg

End of update

All photos, including: before NIR, before custom white balance, and FP NDVi.

Photos of conversion: [For initial conversion for NIR two-camera approach, see prior note].

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For Wratten 25 filter material, see prior note.

First testing image examples of my front yard in Livermore CA were shot after custom white balance in sun using red file folder:

As shot:

12688764185_2c402c901c.jpg

12688762655_41b6ddc794.jpg

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Images processed with Ned Horning Fiji tool with blue channel for NIR and red channel for red; with the Chris Fasti lut. Thanks again to Chris for his helpful comments on the A490 initial test results.

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Questions and next steps

Tune white balance or other parameters to improve results.

Why I'm interested

Continue to explore as tool to assess vegetative health.


12 Comments

Hi, I've also recently posted a research note on NDVI and wratten25 on a cmos sensor. Eventually I got my best results by underexposing slightly and then not stretching the color band. It would be interesting how an image would look on your camera that's slightly underexposed and doesn't stretch the color band. Would you be able to post such an image for comparison?

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I haven't tried to underexpose, but, in update above, did post composite showing effect of not stretching visible band and the NIR band. Doesn't appear conclusive for the specific image processed. Thanks for the feedback

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Great progress Pat. The Wratten 25 photos are really sharp. They should allow very good NDVI images. Also, nice car.

The blemish looks a lot like lens flare. It is weird lens flare, so it is probably being influenced by the new internal filter. I have never noticed that type of lens flare with my converted cameras. It should not be a problem with mapping photos, and an improvised lens hood might eliminate the problem. My to do list includes designing a lens hood to 3D print for protecting the lens from impact and direct sun.

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Thanks Chris. Ah, lens flare. The car is a '94 Miata - good cheap fun.

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Hi there The last post is over a year old so I don't know if there is anyone around to comment

I am new to the IR NDVI scene and along many of the works I have read one of the pictures in this post grabbed my attention, it's the one that starts this post, here the '94 Miata ( the vehicle ) comes out green like if it were a healthy plant.

This grabs my attention because over at a http://agribotic.com they have this article in their blogs where they also show a tractor in green and they know it should not have this color ( Below is the link )

The post can be summarized in regards to the color of the filter to use as

As a practical matter, this translates into Agribotix using a blue notch filter in our cameras and the green channel to serve as the visible signal in vegetation index calculations.

They also use a different formula to get to the best NDIV possibel

DVI is better than DNVI

This is the link http://agribotix.com/blog/2014/6/10/misconceptions-about-uav-collected-ndvi-imagery-and-the-agribotix-experience-in-ground-truthing-these-images-for-agriculture

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I'm still around, but don't have special insight to the points you raise. Consider posting your observations and questions to the PL plots-infrared discussion list which focuses near-infrared imaging and vegetation monitoring discussions; https://groups.google.com/forum/#!forum/plots-infrared.

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Hi Pat

Thanks for your suggestion on the Forum address

I bought a Canon A1200 just like you, and two filters from Cris, one of them the Wratten25, which are on their way.

Regarding your A1200 conversion; after doing it and before putting in the Wratten 25 filter, did you have problems with focusing ? I ask because if the focus on the camera is based on the image or light passing through a filter you are taking out, maybe the focusing gets altered

How about the focusing after placing in the Wratten filter ?

Thank you

Javier

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Javier, Sorry I didn't see this sooner. I've not experienced focus problems with this conversion. Chris is a great resource since he's done so many conversions. Hope you are enjoying the results.

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Thanks for your answer.

BTW THe conversion was very easy, just need to have the tools. Small screwdriver and tweezers to remove the filter in the camera Total time, maybe 10 minutes

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Hi there The last post is over a year old so I don't know if there is anyone around to comment

I'm really wondering that how can I overcome the Miata(vehicle) errror. and the reason what makes such error

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